Young convergent-margin orogens, climate, and crustal thickness—A Late Cretaceous–Paleogene Nevadaplano in the American Southwest?
Young convergent-margin orogens, climate, and crustal thickness—A Late Cretaceous–Paleogene Nevadaplano in the American Southwest?
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年轻的聚合边缘造山带、气候和地壳厚度——美国西南部的晚白垩世-古近纪内华达平原？
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发表时间：
2010
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通讯作者：
W. Ernst
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作者：
W. Ernst
南北走向的安第斯山脉位于东向下降的纳斯卡板块之上的南美洲岩石圈之上。位于南纬25°的科迪勒拉山脉是一个极端干旱的地区，最高的山脉下面覆盖着170公里厚的地壳。相比之下，45°S处的降水充沛的峡湾则由1.35公里厚的地壳支撑。美国西部的喀斯喀特山脉和内华达州山脉显示出类似的南北趋势和纬度降雨模式。西风为西北部提供了充足的水分，但降水量向南减少，在惠特尼山周围的山脉达到最大区域海拔的地方产生了更大的干旱。过度增厚，现在分层，1042 -55公里厚的南部塞拉地壳超过1035公里厚的北方塞拉和活跃的喀斯喀特弧。加州造山带地壳厚度的差异并不像安第斯山脉那样明显，因为谢兰弧的构造在白垩纪末期停止。地质、地球化学和稳定同位素数据表明，在晚白垩世-早第三纪弧的雨影中，内华达高原位于中部+内华达州南部+犹他州西部。40-45公里厚的科罗拉多高原地壳位于南部山脉的下风处，并且，根据它何时升高，它可能代表了在新近纪盆地和山脉延伸期间坍塌的更广泛高地的一部分。
The N-S–trending Andes surmount South American lithosphere above the east-descending Nazca plate. The highest mountains, underlain by ∼70-km-thick crust, cap the Cordillera at 25°S, an extremely arid region. In contrast, the precipitation-drenched fjordland at 45°S is supported by ∼35-km-thick crust. The Cascade and Sierra Nevada ranges in the western United States display comparable N-S trends and latitudinal rainfall patterns. Westerly winds supply abundant moisture to the northwest, but precipitation diminishes southward, producing increased aridity where the Sierra achieves its maximum regional elevation around Mount Whitney. Overthickened, now delaminating, ∼42–55-km-thick crust of the southern Sierra exceeds that of the ∼35-km-thick northern Sierra and the active Cascade arc. Contrasts in orogenic crustal thickness in California are not as marked as in the Andes because Sierran arc construction ceased near the end of Cretaceous time. Geologic, geochemical, and stable isotopic data suggest that a Nevadaplano occupied central + southern Nevada + western Utah in the rain shadow of the Late Cretaceous–Paleogene arc. The ∼40–45-km-thick Colorado Plateau crust lies well downwind from the southern Sierra, and, depending on when it became elevated, it might represent part of a broader highland that collapsed during Neogene Basin and Range extension.